1. Field of the Invention
The present invention relates to a system for efficiently controlling a printing machine which is capable of producing collated sets for in-line finishing of books, proposals, manuals etc with very high productivity.
On-demand page printers, wherein images are created in response to digital image data submitted to the printing apparatus, are familiar in many offices. Such printers create images on sheets typically using electrostatographic or ink-jet printing techniques. In work-set situations, wherein different users at various personal computers and other terminals submit jobs to a single central printing apparatus, various sets of digital image data, corresponding to jobs desired to be printed by different users, are typically kept in an electronic queue, and a control system typically located at the printer sorts through the image data and causes the printer to output the desired prints in an orderly manner.
The terminology “copiers”, and “copies”, as well as “printers” and “prints”, is used alternatively herein. The terminology “imaging” and “marking” is used alternatively herein and refers to the entire process of putting an image (digital or analog source) onto paper. The image can then be permanently fixed to the paper by fusing, drying, or other means. It will be appreciated that the invention may apply to almost any system in which the images are made electronically, including electronic copiers.
Imaging systems (e.g., printers or copiers) typically include copy sheet paper paths through which copy sheets (e.S., plain paper) which are to receive an image are conveyed and imaged. The process of inserting copy sheets into the copy sheet paper path and controlling the movement of the copy sheets through the paper path to receive an image on one or both sides, is referred to as “scheduling”. Copy sheets are printed by being passed through a copy sheet paper path (which includes a marking station) one or multiple times. Copy sheets which are printed on only one side (simplex copy sheets) in a single color usually pass through the copy sheet paper path a single time. Multipass printing is used to print images on both sides of a copy sheet (duplex printing), or to print a simplex sheet in multiple colors (one pass for each color). Particularly with sophisticated printing apparatus, it may often be desired to print “duplex” prints, that is prints having images on both sides of the sheet.
However, most currently available printing devices are capable of producing an image only on one side of a sheet at a time. In order to obtain duplex prints, it is almost always necessary to provide an “inverter” within the printing device or apparatus. The purpose of an inverter is to handle a sheet after one side thereof has received an image, and in effect turn the sheet over to make the remaining blank side available to the same printing apparatus which created the first image. In effect, each duplex print is re-fed past the image-making portion of the printing apparatus so that the individual sheet becomes available to the image-making apparatus twice, once for each side.
In an electro-photographic printing apparatus, wherein images are first created on a photoreceptor in the form of a rotating drum or belt and then transferred to sheets, a key concern is the presence of blank pitches (image-sized spaces) along the drum or belt where, for various reasons relating to the long time required to finish (bind) a set, when no image is created to allow for finisher to complete its operation. The problem with blank pitches is that each blank pitch represents lost productivity. In some cases when the number of sheet in a set are small, the number of blank pitches along the belt may be comparable to the number of pitches actually having images on them. In such a situation, not only is the apparatus effectively running at half-speed, but various mechanical parts associated with the drum or belt will be experiencing wear to no productive purpose. Thus, as a general rule, the overall productivity and reliability of such a printing apparatus is inversely related to the number of blank pitches which result in the printing process.
It is generally known that electronically inputted printers can desirably provide more flexibility in page sequencing (page, copying presentation order) than copiers with physical document sheet input. The printer input is electronically manipulatable electronic page media, rather than physical sheets of paper which are much more difficult to reorder or manipulate into a desired sequence. As also shown in the art noted hereinbelow, it is generally known that certain such reordered or hybrid document page copying orders or sequences may be copied onto a corresponding sequential train of copy sheets in an appropriate copier or-printer to provide higher copying machine productivity yet correct page order copy output, especially for duplex copies made with a copier with trayless duplexing, i.e., providing a limited length endless buffer loop duplexing path for the copy sheets being duplexed.
2. Description of Related Art
It is becoming increasingly common to integrate on-line finishing devices with imaging systems. These on-line finishing devices directly receive copy sheets as they are output from the imaging system and perform various types of finishing operations on each copy sheet, or on each set of copy sheets. The finishing operations can be, for example: binding, stitching, folding, trimming, aligning, rotating, punching, drilling, slitting, perforating, and combinations thereof.
A problem which arises when integrating an existing finishing device with high speed imaging systems is that the finishing device may not be able to receive copy sheets at as high a frequency as the copy sheets can be output by the imaging system. For example, the imaging system described in U.S. Pat. No. 5,095,342 can output copy sheets at a rate of 135-180 per minute when operating in “burst mode”. This rate is too fast for some finishing devices.
One example involves the use of the imaging system disclosed in U.S. Pat. No. 5,095,342 in connection with an on-line Signature Booklet Maker (SBM) to form signature booklets. A “signature” is a duplex printed copy sheet having two page images on each side. The signature sheet can be folded in half to form a booklet, or a plurality of signatures can be aligned, stitched together, and folded in half to form a multi-sheet booklet. Descriptions of signature printing are provided in U.S. Pat. No. 4,727,042 to Smith and U.S. Pat. No. 5,271,065 to Rourke et al., the pertinent portions of which are incorporated herein by reference. The imaging system disclosed in U.S. Pat. No. 5,095,342 is capable of outputting signatures in bursts at a rate of 135 per minute, but the SBM may not be able to receive sheets at such a high rate.
A sheet scheduling approach that compensates for the disparity in sheet handling capabilities of the imaging system and a finishing device, such as the Signature Booklet Maker (SBM), is disclosed in U.S. Pat. No. 5,159,395 to Farrell et al., the pertinent portions of which are incorporated herein by reference. In particular, U.S. Pat. No. 5,159,395 discloses a printing system that operates in one of two modes, depending on whether sheets are being delivered to the SBM. In the first mode, printed copy sheets are output from a copy sheet path of the printing system without any skipped pitches. The first mode of scheduling provides the maximum output (and thus productivity) of the printing system. If, however, the output frequency of the first mode is too great for the finishing device, a second, slower mode of operation results. In the second mode of operation, sheets are output from the printing system with skipped pitches located between at least some of the consecutively output sheets.
Another approach which compensates for the disparity in sheet handling capabilities of the imaging system and a finishing device is disclosed in U.S. Pat. No. 4,782,363 to Britt et al. The system of U.S. Pat. No. 4,782,363 comprises a collating and finishing apparatus and method including a buffered design to allow more time to finish a copy set without halting copying. In a pre-collation copying mode, two bins at a time are utilized as the buffer for compiling while one or two other bins are awaiting being emptied for finishing, and then they function as the buffer for the next two copy sets, etc. A key feature of the system, which enhances productivity, is the sequential use of different pairs of three compiler bins in coordination with finishing so that while the second of one pair of copy sheets is being removed from a bin and finished, the first two sheets of the next sequence or set are entering two other now empty and available bins, in a continuous enter one side/exit the other side sequential operation.
Some examples of other prior art copiers, and especially with control systems therefor, including operator console switch selection inputs, document sheet detecting switches, etc., are disclosed in U.S. Pat. Nos.: 4,054,380; 4,062,061; 4,076,408; 4,078,787; 4,099,860; 4,125,325; 4,132,401; 4,144,550; 4,158,500; 4,176,945; 4,179,215; 4,229,101; 4,278,344; 4,284,270; and 4,475,156.
While the approaches of U.S. Pat. No. 4,782,363 and U.S. Pat. No. 5,159,395 enhance printing system productivity, each approach experiences loss of imaging system productivity under certain circumstances. Regarding U.S. Pat. No. 4,782,363, if a pair of bins cannot be emptied out by the time another set is to be delivered, then the imaging system must skip pitches. Regarding U.S. Pat. No. 5,159,395, the printing system operates in a degraded mode, in which pitches must be skipped, when sheets are being delivered to the finishing device. Regarding U.S. Pat. No. 5,452,068, an alternate output tray or an alternate finishing device is needed to improve productivity.
U.S. Pat. No. 5,452,068 describes a technique for finishing print jobs by scheduling for delivery to a portion of the first job to an in-line finisher and a second job, scheduled for delivery to a second destination (an output tray), in a manner that reduces productivity losses in a marking engine. A difficulty with prior art systems is an inability to prioritize jobs ready to print and to be able to run and complete one or several small jobs during the processing of a very high volume job and being able to blend jobs into the same finishing device.
It would be desirable, therefore, to be able to look ahead at a job queue, find one or more suitable jobs in the queue(for example, jobs that can be delivered to the same output device), and be able to concurrently run multiple jobs to improve productivity.
It is an object of the present invention, therefore, to be able to scan a job queue during the processing of a first job and while processing the first job, being able to intermix the concurrent processing of multiple jobs delivered to the same output (finishing) station.
However, it would be desirable to provide a system in which imaging system productivity is increased, relative to the above-discussed references.
It is well known in this art, and in general, how to program and execute document handler and copier control functions and logic with conventional or simple software instructions for conventional microprocessors in a copier controller. This is taught by the above and other patents and various commercial copiers. Such software may vary depending on the particular function and particular microprocessor or microcomputer system utilized, of course, but will be available to or readily programmable by those skilled in the applicable arts without experimentation, from either descriptions or prior knowledge of the desired functions together with general knowledge in the general software and computer arts. It is also known that conventional or specified document and copy sheet handling functions and controls may be alternatively conventionally provided utilizing various other known or suitable logic or switching systems.